(C0)polymerization of vinyl chloride in the presence of a stable nitroxyl radical

ABSTRACT

The present invention pertains to a process for controlled free radical polymerization or copolymerization of vinyl chloride at a temperature between 40° C. and 95° C., at a pressure between 5 and 30 bar in the presence of a stable free nitroxyl radical.

[0001] The present invention relates to the polymerization orcopolymerization of vinyl chloride in the presence of a stable freenitroxyl radical. Further subjects of the invention are the use ofstable free nitroxyl radicals as polymerization regulators for freeradical polymerization of vinyl chloride and a polyvinyl chloridemacroinitiator having a thermally labile bound nitroxyl group, capableto be split upon thermal treatment into a nitroxyl radical and apolymeric/oligomeric radical.

[0002] Polyvinyl chloride (PVC) holds a unique position amongst all thepolymers produced. It is rather inexpensive and is used in such a widerange of applications that its versatility is almost unlimited.Depending on its molecular weight, additives and stabilizers, theapplications range from rigid pipes and profiles to very soft,transparent and flexible films.

[0003] PVC can be produced from vinyl chloride monomer (VCM) by threedifferent processes. The most widely used is the suspension typepolymerization, which accounts for approximately 75%. Droplets of liquidvinyl chloride are dispersed in water using a protective colloid in anagitated reactor. Polymerization occurs inside the droplets as a resultof the use of an oil-soluble initiator. The product is in the form of100-150 μm diameter porous grains. Another process is the emulsionroute, in which the monomer is dispersed in water, using agitation andpowerful surfactants and the polymerization is carried out in theaqueous phase, using a water soluble initiator. The polymerizationproduct is in the form of an aqueous latex dispersion of PVC particles0.1-2.0 μm in diameter. These are spray-dried to form largeragglomerates, which are milled before being dispersed in solvents andplasticizers to give plastisols, used in a variety of spreading anddipping applications. The third route is bulk or mass polymerization. Asthe name implies the polymerization is carried out in vinyl chloride(VCM) in the absence of water. A review of the manufacturing of PVC isfor example described in Encyclopedia of Polymer Science andEngineering, second edition, vol. 17, pages 295-376.

[0004] Controlled radical polymerization of ethylenically unsaturatedmonomers in the presence of a nitroxyl radical is principally known andfor example described in U.S. Pat. No. 5,322,912 to Georges et al.issued Jun. 21, 1994. U.S. Pat. No. 5,322,912 discloses a polymerizationprocess using a free radical initiator, a polymerizable monomer compoundand a stable free radical agent of the basic structure R′R″N—O. for thesynthesis of homopolymers and block copolymers of for example styrene.So far there is no process described in the prior art for thepolymerization or copolymerization of vinyl chloride in the presence ofnitroxyl radicals.

[0005] Since the polymerization of PVC is essentially based on thetransfer reaction of chlorine radicals one would expect, that nitroxylradicals lead to a reduction of the molecular weight, because they aretheoretically capable of reacting with the chlorine radicals. Inparticular since nitroxyl radicals have been suggested as short stoppingagents for use in the polymerization of vinyl monomers such as styrene.

[0006] It has now been found that the polymerization of vinyl chlorideis not adversely affected by stable free nitroxyl radicals. On thecontrary in the presence of a stable free nitroxyl radical, molecularweights remain high at relatively high polymerization temperatures,thereby allowing the production of high molecular weight polymers athigh polymerization temperatures. This is in contrast to classical PVCpolymerization, where increasing temperature results in lower molecularweight. On the other hand polydispersity (PD) of the PVC decreases,indicating a control of the polymerization reaction by the nitroxylradicals. A lower polydispersity is desirable since the polymer containsless low molecular weight portions, which can be advantageous, forexample, for the mechanical properties of the polymer. Nitroxyl radicalsare attached to the PVC backbone thereby allowing a subsequent furtherradical polymerization starting from the PVC backbone by splitting intoa macroradical and a nitroxyl radical upon thermal treatment. This isalso called reinitiation. The PVC backbone can be seen as amacroinitiator onto which a second block can be polymerized. This openstotally new opportunities for the production of block copolymers withPVC as one block.

[0007] One subject of the invention is a process for controlled freeradical polymerization or copolymerization of vinyl chloride at atemperature between 40° C. and 95° C., at a pressure between 5 and 30bar in the presence of a stable free nitroxyl radical.

[0008] Preferably the polymerization or copolymerization is carried outin suspension.

[0009] The suspension polymerization process is essentially a bulkpolymerization process carried out in millions of small “reactors”(droplets). Liquid vinyl chloride under its autogeneous vapor pressureis dispersed in water by vigorous stirring in a reactor (autoclave).This results in the formation of droplets of for example an average sizebetween 30-40 μm which are stabilized against coalescence by one or moreprotective colloids (granulating agents). The other essential ingredientis a monomer-soluble free radical initiator. Typically such a basicformulation, also called recipe, can contain 100 parts vinyl chloride,90-130 parts water, 0.05-0.15 parts protective colloid and 0.03-0.08parts radical initiator. To achieve the optimum morphology otheradditives have to be employed, such as oxygen, buffers, secondary ortertiary granulating agents, chain transfer or chain extending agents,comonomers and antioxidants.

[0010] Typical protective colloids are cellulose ether derivatives,partially hydrolyzed polyvinyl acetates or polyvinyl alcohols. Examplesfor cellulose ethers are hydroxypropylmethylcellulose,hydroxyethyl-cellulose, hydroxypropyl-cellulose or methyl-cellulose.

[0011] Typical radical initiators are diacyl peroxides such as dilauroylperoxide, peroxodicarbonates, such as dicyclohexyl peroxodicarbonate ordicetyl peroxodicarbonate, alkyl peroxyesters, such ast-butylperoxypivalate or α-cumyl perneodecanoate and azo initiators,such as azobisisobutyronitrile. It is advantageous to select aninitiator with a half life of 1-10 hours, preferably 2-5 hours at thepolymerization temperature.

[0012] Although the stable free nitrogen radical may be added not onlyat the beginning of the reaction, but also in a later stage wherepolymerization has already proceeded to some extent, it is preferablyadded before 10% of polymer formation has occurred and more preferablyadded directly to the recipe at the beginning of the polymerization.

[0013] Preferred is a process, wherein the free radical initiator ispresent in an amount of from 0.001 mol % to 5 mol %, more preferred0.005 to 1 mol %, based on the monomer.

[0014] Typically the amount of stable free nitroxyl radical is from0.001 to 1 mol 5 based on the monomer.

[0015] Preferably the molar ratio of free radical initiator to stablefree nitroxyl radical is from 100:1 to 1:10, more preferably from 10:1to 1:2.

[0016] It is also possible to add to the initial recipe a nitroxyletherR′R″N—O—X, where X represents a group having at least one carbon atomand is such that a free radical X. derived from X is formed under thereaction conditions applied. The formation of an additional free radicalX. may in the case of vinyl chloride enhance the radical polymerizationinitiated by the free radical initiator, whereas its counterpart, thenitroxyl radical, can act as controlling agent. Nitroxylethers of thegeneric formula R′R″N—O—X and their use as initiating and polymerizationcontrolling agents have first been described in U.S. Pat. No. 4,581,429by Solomon.

[0017] Hence a process, wherein the stable free nitroxyl radical isformed in situ during the polymerization reaction from the correspondingnitroxylether is also a preferred embodiment of the present invention.

[0018] Preferably the polydispersity of the polyvinyl chloride is from1.1 to 2.5, more preferably from 1.1 to 2.0.

[0019] Many attempts have been made in the last years to find newversatile stable free nitroxyl radicals or nitroxyl ethers which improvefor example conversion rate however retaining the advantages ofcontrolled polymerization as for example low polydispersity and thecapability of block copolymer formation. Many improvements have beenmade by modifying the chemical structure of the nitroxyl radical or ofthe nitroxyl ether. All these prior art compounds are principallysuitable for controlled polymerization of vinyl chloride.

[0020] WO 98/13392 for example describes open chain alkoxyaminecompounds which have a symmetrical substitution pattern and are derivedfrom nitroso compounds.

[0021] WO 96/24620 describes a polymerization process in which veryspecific stable free radical agents are used, such as for example

[0022] WO 98/30601 discloses specific nitroxyls based onimidazolidinons.

[0023] WO 98/44008 discloses specific nitroxyls based on morpholinones,piperazinones and piperazindiones.

[0024] Further suitable nitroxylethers and nitroxyl radicals areprincipally known from U.S. Pat. No. 4,581,429 or EP-A-621 878.Particularly useful are the open chain compounds described in WO99/03894 and WO 00/07981, the piperidine derivatives described in WO99/67298 and GB 2335190 or the heterocyclic compounds described in GB2342649 and WO 96/24620.

[0025] Particularly useful are stable free nitroxyl radicals of formulaA′, B′ or O′,

[0026] wherein

[0027] m is 1,

[0028] R is hydrogen, C₁-C₁₈alkyl which is uninterrupted or interruptedby one or more oxygen atoms, cyanoethyl, benzoyl, glycidyl, a monovalentradical of an aliphatic carboxylic acid having 2 to 18 carbon atoms, ofa cycloaliphatic carboxylic acid having 7 to 15 carbon atoms, or anα,β-unsaturated carboxylic acid having 3 to 5 carbon atoms or of anaromatic carboxylic acid having 7 to 15 carbon atoms;

[0029] p is 1;

[0030] R₁₀₁ is C₁-C₁₂alkyl, C₅-C₇cycloalkyl, C₇-C₈aralkyl,C₂-C₁₈alkanoyl, C₃-C₅alkenoyl or benzoyl;

[0031] R₁₀₂ is C₁-C₁₈alkyl, C₅-C₇cycloalkyl, C₂-C₈alkenyl unsubstitutedor substituted by a cyano, carbonyl or carbamide group, or is glycidyl,a group of the formula —CH₂CH(OH)—Z or of the formula —CO-Z or —CONH-Zwherein Z is hydrogen, methyl or phenyl;

[0032] G₆ is hydrogen and G₅ is hydrogen or C₁-C₄alkyl, and

[0033] G₁ and G₃ are methyl and G₂ and G₄ are ethyl or propyl or G₁ andG₂ are methyl and G₃ and G₄ are ethyl or propyl.

[0034] Preferably in formula A′, B′ and O′R is hydrogen, C₁-C₁₈alkyl,cyanoethyl, benzoyl, glycidyl, a monovalent radical of an aliphatic,carboxylic acid;

[0035] R₁ is C₁-C₁₂alkyl, C₇-C₈aralkyl, C₂-C₁₈alkanoyl, C₃-C₅alkenoyl orbenzoyl;

[0036] R₂ is C₁-C₁₈alkyl, glycidyl, a group of the formula —CH₂CH(OH)-Zor of the formula —CO-Z,

[0037] wherein Z is hydrogen, methyl or phenyl.

[0038] The above compounds and their preparation is described in GB2335190.

[0039] Another preferred group of nitroxyl radicals are those of formula(Ic′), (Id′), (Ie′), (If′), (Ig′) or (Ih′)

[0040] wherein R₁, R₂, R₃ and R₄ independently of each other areC₁-C₁₈alkyl, C₃-C₁₈alkenyl, C₃-C₁₈alkinyl, C₁-C₁₈alkyl, C₃-C₁₈alkenyl,C₃-C₁₈alkinyl which are substituted by OH, halogen or a group—O—C(O)—R₅, C₂-C₁₈alkyl which is interrupted by at least one O atomand/or NR₅ group, C₃-C₁₂cycloalkyl or C₆-C₁₀aryl or R₁ and R₂ and/or R₃and R₄ together with the linking carbon atom form a C₃-C₁₂cycloalkylradical;

[0041] R₅, R₆ and R₇ independently are hydrogen, C₁-C₁₈alkyl orC₆-C₁₀aryl;

[0042] R₈ is hydrogen, OH, C₁-C₁₈alkyl, C₃-C₁₈alkenyl, C₃-C₁₈alkinyl,C₁-C₁₈alkyl, C₃-C₁₈alkenyl, C₃-C₁₈-alkinyl which are substituted by oneor more OH, halogen or a group —O—C(O)—R₅, C₂-C₁₈alkyl which isinterrupted by at least one O atom and/or NR₅ group, C₃-C₁₂cycloalkyl orC₆-C₁₀aryl, C₇-C₉phenylalkyl, C₅-C₁₀heteroaryl, —C(O)—C₁-C₁₈alkyl,—O—C₁-C₁₈alkyl or —COOC₁-C₁₈alkyl; and

[0043] R₉, R₁₀, R₁₁, and R₁₂ are independently hydrogen, phenyl orC₁-C₁₈alkyl.

[0044] Preferably in formula (Ic′), (Id′), (Ie′), (If′), (Ig′) and (Ih′)at least two of R₁, R₂, R₃ and R₄ are ethyl, propyl or butyl and theremaining are methyl; or

[0045] R₁ and R₂ or R₃ and R₄ together with the linking carbon atom forma C₅-C₆cycloalkyl radical and one of the remaining substituents isethyl, propyl or butyl.

[0046] The above compounds and their preparation is described in GB2342649.

[0047] Yet another preferred group of compounds are those wherein thestable free nitroxyl radical has a hydrogen atom bound to the carbonatom in α-position to the nitrogen atom. Examples and their preparationare given in WO 00/53640.

[0048] When nitroxyl ethers are used, those are preferred which leadafter cleavage to the above mentioned nitroxyl radicals.

[0049] Particularly preferred are the nitroxyl ether of formula A, B orO,

[0050] wherein

[0051] m is 1,

[0052] R is hydrogen, C₁-C₁₈alkyl which is uninterrupted or interruptedby one or more oxygen atoms, cyanoethyl, benzoyl, glycidyl, a monovalentradical of an aliphatic carboxylic acid having 2 to 18 carbon atoms, ofa cycloaliphatic carboxylic acid having 7 to 15 carbon atoms, or anα,β-unsaturated carboxylic acid having 3 to 5 carbon atoms or of anaromatic carboxylic acid having 7 to 15 carbon atoms;

[0053] p is 1;

[0054] R₁₀₁ is C₁-C₁₂alkyl, C₅-C₇cycloalkyl, C₇C₈aralkyl,C₂-C₁₈alkanoyl, C₃-C₅alkenoyl or benzoyl;

[0055] R₁₀₂ is C₁-C₁₈alkyl, C₅-C₇cycloalkyl, C₂-C₈alkenyl unsubstitutedor substituted by a cyano, carbonyl or carbamide group, or is glycidyl,a group of the formula —CH₂CH(OH)-Z or of the formula —CO-Z or —CONH-Zwherein Z is hydrogen, methyl or phenyl;

[0056] G₆ is hydrogen and G₅ is hydrogen or C₁-C₄alkyl,

[0057] G₁ and G₃ are methyl and G₂ and G₄ are ethyl or propyl or G₁ andG₂ are methyl and G₃ and G₄ are ethyl or propyl; and

[0058] X is selected from the group consisting of

[0059] —CH₂-phenyl, CH₃CH-phenyl, (CH₃)₂C-phenyl, (C₅-C₆cycloalkyl)₂CCN,(CH₃)₂CCN, CH₂CH═CH₂, CH₃CH—CH═CH₂ (C₁-C₄alkyl)CR₂₀—C(O)-phenyl,(C₁-C₄)alkyl-CR₂₀—C(O)-(C₁-C₄)alkoxy,(C₁-C₄)alkyl-CR₂₀—C(O)—(C₁-C₄)alkyl,(C₁-C₄)alkyl-CR₂₀—C(O)—N-di(C₁-C₄)alkyl,(C₁-C₄)alkyl-CR₂₀—C(O)—NH(C₁-C₄)alkyl, (C₁-C₄)alkyl-CR₂₀—C(O)—NH₂,wherein

[0060] R₂₀ is hydrogen or (C₁-C₄)alkyl.

[0061] More preferred are compounds, wherein in formula A, B and O

[0062] R is hydrogen, C₁-C₁₈alkyl, cyanoethyl, benzoyl, glycidyl, amonovalent radical of an aliphatic, carboxylic acid;

[0063] R₁₀₁ is C₁-C₁₂alkyl, C₇-C₈aralkyl, C₂-C₁₈alkanoyl, C₃-C₅alkenoylor benzoyl;

[0064] R₁₀₂ is C₁-C₁₈alkyl, glycidyl, a group of the formula—CH₂CH(OH)-Z or of the formula —CO-Z wherein Z is hydrogen, methyl orphenyl; and

[0065] X is CH₃CH-phenyl.

[0066] These compounds and their preparation is described in GB 2335190.

[0067] Equally preferred is a process wherein the nitroxyl ether fromwhich the stable free nitroxyl radical is formed is of formula (Ic),(Id), (Ie), (If), (Ig) or (Ih)

[0068] wherein R₁, R₂, R₃ and R₄ independently of each other areC₁-C₁₈alkyl, C₃-C₁₈alkenyl, C₃C₁₈alkinyl, C₁-C₁₈alkyl, C₃-C₁₈alkenyl,C₃-C₁₈alkinyl which are substituted by OH, halogen or a group—O—C(O)—R₅, C₂-C₁₈alkyl which is interrupted by at least one O atomand/or NR₅ group, C₃-C₁₂cycloalkyl or C₆-C₁₀aryl or R₁ and R₂ and/or R₃and R₄ together with the linking carbon atom form a C₃-C₁₂cycloalkylradical;

[0069] R₅, R₆ and R₇ independently are hydrogen, C₁-C₁₈alkyl orC₆-C₁₀aryl;

[0070] R₈ is hydrogen, OH, C₁-C₁₈alkyl, C₃-C₁₈alkenyl, C₃-C₁₈alkinyl,C₁-C₁₈alkyl, C₃-C₁₈alkenyl, C₃-C₁₈alkinyl which are substituted by oneor more OH, halogen or a group —O—C(O)—R₅, C₂-C₁₈alkyl which isinterrupted by at least one O atom and/or NR₅ group, C₃-C₁₂cycloalkyl orC₆-C₁₀aryl, C₇-C₉phenylalkyl, C₅-C₁₀heteroaryl, —C(O)—C₁-C₁₈alkyl,—O—C₁-C₁₈alkyl or —COOC₁-C₁₈alkyl;

[0071] R₉, R₁₀, R₁₁ and R₁₂ are independently hydrogen, phenyl orC₁-C₁₈alkyl; and

[0072] X is selected from the group consisting of —CH₂-phenyl;CH₃CH-phenyl, (CH₃)₂C-phenyl, (C₅-C₆cycloalkyl)₂CCN, (CH₃)₂CCN,—CH₂CH═CH₂, CH₃CH—CH═CH₂ (C₁-C₄alkyl)CR₂₀—C(O)phenyl,(C₁-C₄)alkyl-CR₂₀—C(O)—(C₁-C₄)alkoxy,(C₁-C₄)alkyl-CR₂₀—C(O)—(C₁-C₄)alkyl,(C₁-C₄)alkyl-CR₂₀—C(O)—N-di(C₁-C₄)alkyl,(C₁-C₄)alkyl-CR₂₀—C(O)—NH(C₁-C₄)alkyl, (C₁-C₄)alkyl-CR₂₀—C(O)—NH₂,wherein R₂₀ is hydrogen or (C₁-C₄)alkyl.

[0073] Most preferred are compounds wherein in formula (Ic), (Id), (Ie),(If), (Ig) and (Ih) at least two of R₁, R₂, R₃ and R₄ are ethyl, propylor butyl and the remaining are methyl; or

[0074] R₁ and R₂ or R₃ and R₄ together with the linking carbon atom forma C₅-C₆cycloalkyl radical and one of the remaining substituents isethyl, propyl or butyl.

[0075] The alkyl radicals in the various substituents may be linear orbranched. Examples of alkyl containing 1 to 18 carbon atoms are methyl,ethyl, propyl, isopropyl, butyl, 2-butyl, isobutyl, t-butyl, pentyl,2-pentyl, hexyl, heptyl, octyl, 2-ethylhexyl, t-octyl, nonyl, decyl,undecyl, dodecyl, tridecyl, tetradecyl, hexadecyl and octadecyl.

[0076] Alkenyl with 3 to 18 carbon atoms is a linear or branched radicalas for example propenyl, 2-butenyl, 3-butenyl, isobutenyl,n-2,4-pentadienyl, 3-methyl-2-butenyl, n-2-octenyl, n-2-dodecenyl,iso-dodecenyl, oleyl, n-2-octadecenyl oder n-4-octadecenyl. Preferred isalkenyl with 3 bis 12, particularly preferred with 3 to 6 carbon atoms.

[0077] Alkinyl with 3 to 18 is a linear or branched radical as forexample propinyl (—CH₂—C≡CH), 2-butinyl, 3-butinyl, n-2-octinyl, odern-2-octadecinyl. Preferred is alkinyl with 3 to 12, particularlypreferred with 3 to 6 carbon atoms.

[0078] Examples for hydroxy substituted alkyl are hydroxy propyl,hydroxy butyl or hydroxy hexyl.

[0079] Examples for halogen substituted alkyl are dichloropropyl,monobromobutyl or trichlorohexyl.

[0080] C₂-C₁₈alkyl interrupted by at least one O atom is for example—CH₂—CH₂—O—CH₂—CH₃, —CH₂—CH₂—O—CH₃— or —CH₂CH₂—CH₂—CH₂—CH₂O—CH₂—CH₃—. Itis preferably derived from polyethlene glycol. A general description is—((CH₂)_(a)—O)_(b)—H/CH₃, wherein a is a number from 1 to 6 and b is anumber from 2 to 10.

[0081] C₂-C₁₈alkyl interrupted by at least one NR₅ group may begenerally described as —((CH₂)₃—NR₅)_(b)—H/CH₃, wherein a, b and R₅ areas defined above.

[0082] C₃-C₁₂cycloalkyl is typically, cyclopropyl, cyclopentyl,methylcyclopentyl, dimethylcyclopentyl, cyclohexyl, methylcyclohexyl ortrimethylcyclohexyl.

[0083] C₆-C₁₀ aryl is for example phenyl or naphthyl, but also comprisedare C₁-C₄alkyl substituted phenyl, C₁-C₄alkoxy substituted phenyl,hydroxy, halogen or nitro substituted phenyl. Examples for alkylsubstituted phenyl are ethylbenzene, toluene, xylene and its isomers,mesitylene or isopropylbenzene. Halogen substituted phenyl is forexample dichlorobenzene or bromotoluene.

[0084] Alkoxy substituents are typically methoxy, ethoxy, propoxy orbutoxy and their corresponding isomers.

[0085] C₇-C₉phenylalkyl is benzyl, phenylethyl or phenylpropyl.

[0086] C₅-C₁₀heteroaryl is for example pyrrol, pyrazol, imidazol, 2,4,dimethylpyrrol, 1-methylpyrrol, thiophene, furane, furfural, indol,cumarone, oxazol, thiazol, isoxazol, isothiazol, triazol, pyridine,α-picoline, pyridazine, pyrazine or pyrimidine.

[0087] If R is a monovalent radical of a carboxylic acid, it is, forexample, an acetyl, propionyl, butyryl, valeroyl, caproyl, stearoyl,lauroyl, acryloyl, methacryloyl, benzoyl, cinnamoyl orβ-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl radical.

[0088] C₁-C₁₈alkanoyl is for example, formyl, propionyl, butyryl,octanoyl, dodecanoyl but preferably acetyl and C₃-C₅alkenoyl is inparticular acryloyl.

[0089] Particularly suitable nitroxylethers and nitroxyl radicals arethose of formulae

[0090] The process is particularly useful for the preparation of blockcopolymers, wherein in a first step vinyl chloride is polymerized and ina second step a different ethylenically unsaturated monomer is added tothe polyvinyl chloride and block copolymerized to form an A-B block.

[0091] It is also possible to repeat the procedure two, three or moretimes and to arrive at multi-block structures.

[0092] When copolymers are made, they may be of statistical copolymerstructure, tapered structure or multiblock copolymer structure such asA-B-A, B-A-B or A-B-C. The length of the blocks may vary in a widerange. It may be sufficient to influence the polymer properties, such aspolyrity, compatibility or adhesion if the second block consists forexample of one to a few monomer units. For the modification of otherproperties, such as glass transition temperatures or mechanicalproperties a block length of more than 5 units is preferable.

[0093] Preferably the different ethylenically unsaturated monomer isselected from the group consisting of ethylene, propylene, n-butylene,i-butylene, styrene, substituted styrene, vinylpyridine, conjugateddienes, acrolein, vinyl acetate, vinylpyrrolidone, vinylimidazole,maleic anhydride, maleinimide which may be unsubstituted at the nitrogenatom or substituted by alkyl or aryl, (alkyl)acrylic acidanhydrides,(alkyl)acrylic acid salts, (alkyl)acrylicacid esters,(alkyl)acrylonitriles or (alkyl)acrylamides.

[0094] For example the ethylenically unsaturated monomer is a compoundof formula CH₂═C(R_(a))—(C=Z)-R_(b), wherein R_(a) is hydrogen orC₁-C₄alkyl, R_(b) is NH₂, O⁻(Me⁺), glycidyl, unsubstituted C₁-C₁₈alkoxy,C₂-C₁₀₀alkoxy interrupted by at least one N and/or O atom, orhydroxy-substituted C₁-C₁₈alkoxy, unsubstituted C₁-C₁₆alkylamino,di(C₁-C₁₈alkyl)amino, hydroxy-substituted C₁-C₁₈alkylamino orhydroxy-substituted di(C₁-C₁₈alkyl)amino, —O—CH₂CH₂—N(CH₃)₂ or—O—CH₂—CH₂—N⁺H(CH₃)₂ An⁻;

[0095] An⁻ is a anion of a monovalent organic or inorganic acid;

[0096] Me is a monovalent metal atom or the ammonium ion.

[0097] Z is oxygen or sulfur.

[0098] Examples of acids from which the anion An⁻ is derived areC₁-C₁₂carboxylic acids, organic sulfonic acids such as CF₃SO₃H orCH₃SO₃H, mineralic acids such as HCl, HBr or HI, oxo acids such as HClO₄or complex acids such as HPF₆ or HBF₄.

[0099] Examples for R_(b) as C₂-C₁₀₀alkoxy interrupted by at least one Oatom are of formula

[0100] wherein R_(c) is C₁-C₂₅alkyl, phenyl or phenyl substituted byC₁-C₁₈alkyl, R_(d) is hydrogen or methyl and v is a number from 1 to 50.These monomers are for example derived from non ionic surfactants byacrylation of the corresponding alkoxylated alcohols or phenols. Therepeating units may be derived from ethylene oxide, propylene oxide ormixtures of both.

[0101] Further examples of suitable acrylate or methacrylate monomersare given below.

[0102] An⁻, wherein An⁻ and R_(a) have the meaning as defined above andR_(e) is methyl or benzyl. An⁻ is preferably Cl⁻, Br⁻ or ⁻O₃S—CH₃.

[0103] Further acrylate monomers are

[0104] Examples for suitable monomers other than acrylates are

[0105] wherein R is H, C₁-C₁₂alkyl or phenyl.

[0106] Preferably R_(a) is hydrogen or methyl, R_(b) is NH₂, gycidyl,unsubstituted or with hydroxy substituted C₁-C₄alkoxy, unsubstitutedC₁-C₄alkylamino, di(C₁-C₄alkyl)amino, hydroxy-substitutedC₁-C₄alkylamino or hydroxy-substituted di(C₁-C₄alkyl)amino; and Z isoxygen.

[0107] Most preferably the ethylenically unsaturated monomer is anacrylic acid ester, acrylamide, acryinitrile, methacrylic acid ester,methacrylamide, methacryinitrile, butadiene, isoprene or maleinimide.

[0108] The block copolymer can be prepared by first isolating thepolyvinyl chloride and subsequent purification if necessary. Thepolyvinyl chloride is then dissolved or dispersed in a suitable solventor in the monomer in a reactor. If not yet present, the monomer is addedand the mixture is stirred under heating. Depending on the nitroxylradical and the monomer used, a temperature from 90° C. to 160° C. maybe necessary to initiate polymerization of the second block. Preferablythe temperature is from 90° C. to 150° C. Other polymerizationprocesses, such as emulsion, suspension or microemulsion are alsopossible.

[0109] It may be useful to carry out the second polymerization step inthe presence of a PVC stabilizer to avoid thermal degradation of PVC,especially at higher reaction temperatures. Such stabilizers are forexample Ca, Zn, Ba or Cd salts of carbonic acids. Preferred PVCstabilizers do not interfere with the radical polymerization process.Suitable stabilizers are for example mixed metal stabilizers, forexample on the basis of Ca and Zn. Suitable stabilizers are described in“Plastic Additives Handbook, 5th Edition, 2000, pages 427-465”.

[0110] In many cases isolation and purification of the polyvinylchloride is not necessary and the second monomer can be added directlyto the reactor wherein the vinyl chloride has been polymerized afterexcess vinyl chloride has been removed.

[0111] The possibility of reinitiating polymerization is a uniquefeature of a so called “living” polymerization.

[0112] Consequently a further subject of the invention is a polyvinylchloride macroinitiator having bound a thermally labile nitroxyl groupvia the oxygen atom, said macroinitiator being able to split into apolyvinyl chloride radical and a nitroxyl radical upon thermaltreatment.

[0113] Still another subject of the invention is the use of a stablefree nitroxyl radical for controlled free radical polymerization orcopolymerization of vinyl chloride at a temperature between 40° C. and95° C., at a pressure between 5 and 30 bar.

[0114] Light and heat stabilizers and, if desired, further additives maybe added to the polyvinylchloride (PVC) prepared by the instant process.These may be mixed with the PVC using equipment known per se, such ascalenders, mixers, compounders, extruders and the like.

[0115] The polyvinylchloride prepared in accordance with the presentinvention can be converted into the desired shape in a known manner.Methods of this type are, for example, grinding, calendering, extrusion,injection moulding, sintering or spinning, furthermore extrusion blowmoulding or conversion by the plastisol process. It can also beconverted into foams.

[0116] The polyvinylchloride prepared according to the invention isparticularly suitable for semirigid and flexible formulations, inparticular in the form of flexible formulations for wire sheaths andcable insulations, which is particularly preferred. In the form ofsemirigid formulations it is particularly suitable for decorative films,foams, agricultural sheeting, tubes, sealing profiles and office films.

[0117] In the form of rigid formulations it is particularly suitable forhollow articles (bottles), packaging films (thermoformed films), blownfilms, crash-pad films (automobiles), tubes, foams, heavy profiles(window frames), light-wall profiles, building profiles, sidings,fittings, office films and equipment housings (computers and domesticapplicances).

[0118] Examples of the use of the polyvinylchloride as plastisols areartificial leather, floor coverings, textile coatings, wall coverings,coil coatings and automobile underseal. The following examplesillustrate the invention.

GENERAL EXPERIMENTAL DESCRIPTION OF EXAMPLES 1 THROUGH 9 AND CONTROLEXPERIMENTS A THROUGH D

[0119] The polymerization is carried out according to the suspensionprocess in batch operation. A double jacketed pressure reactor isoperated at a temperature between 70° C. and 85° C. The reactor volumeis 500 ml, stirrer velocity 1000 rpm, the pressure amounts to 12-18 bardepending on the temperature used for polymerization.

[0120] The following recipe is added into the reactor

[0121] 250 ml H₂O demineralized and degassed

[0122] 62.5 g (1 mol) vinyl chloride 3.7, 99.97% stabilized (supplier:Messer Griesheim)

[0123] 234 mg polyvinylalkohol 7200, degree of hydrolysis 98% (supplierMerck Schuchard)

[0124] 30 mg citric acid

[0125] 0.1 mol % based on vinyl chloride of1,1-dimethyl-2-ethylhexaneperoxoat (Luperox® Elf Atochem)

[0126] Molecular weights are determined by gel permeation chromatography(GPC) using tetrahydrofurane as eluens, based on polystyrene standards(3 columns, Polymer Laboratories).

[0127] The stable free nitroxyl radicals added to the recipe are givenin Tables 1-4. TABLE 1 Influence of temperature on polymerization in thepresence of nitroxyl 1 PD No. T (° C.) yield (%) Mn Mw (Mw/Mn) control A75 89 31000 72000 2.3 control B 80 88 25000 58000 2.3 control C 85 7118000 47000 2.7 example 1 75 57 29000 64000 2.2 example 2 80 63 2900056000 1.9 example 3 85 57 24000 50000 2.1

[0128] TABLE 2 Influence of nitroxyl concentration using nitroxyl 1Nitroxyl concentration T yield PD No. (mol %) (° C.) (%) Mn Mw (Mw/Mn)control D — 80 76 19000 51000 2.7 example 4 0.025 85 56 20000 45000 2.2example 5 0.030 85 65 20000 44000 2.2 example 6 0.050 85 42 19000 420002.3 example 7 0.075 85 38 17000 40000 2.3

[0129] TABLE 3 Influence of nitroxyl type Nitroxyl radical 0.05 mol % onvinyl No. chloride T (° C.) yield (%) Mn Mw PD (Mw/Mn) control B — 80 8825000 58000 2.3 example 8 nitroxyl 2 80 64 22000 51000 2.3 example 9nitroxyl 3 80 74 20000 46000 2.2 stable free nitroxyl radicals:

reaction time: 21 h

GENERAL EXPERIMENTAL Description Of Examples 10 Through 14 And CONTROLEXPERIMENTS E, F

[0130] The polymerization is carried out according to the suspensionprocess in batch operation. A double jacketed pressure reactor of avolume of 1000 ml is operated at a temperature between 70° C. and 90° C.at a stirrer velocity of 1000 rpm. The pressure amounts to 9-18 bardepending on the temperature used for the polymerization.

[0131] The following recipe is added into the reactor:

[0132] 200 ml H₂O demineralized and degassed

[0133] 75 g vinyl chloride 3.7, 99.97% stabilized (supplier MesserGriesheim),

[0134] 300 mg polyvinylalcohol (mowiol 8-88, supplier Clariant)

[0135] 0.1 mol-% based on vinyl chloride of1,1-dimethyl-2-ethylhexaneperoxoat (Luperox 26, supplier. Atofina)

[0136] After a reaction time of 21 hours, the obtained polymer isisolated by filtration or centrifugation. The crude polymer is washedwith water, filtered, washed with ethanol, dried under vacuum at 40° C.until constant weight.

[0137] Molecular weights and polydispersity are determined by GPC (3columns, PL Polymer Laboratories), calibrated with narrow distributedpolystyrene standards.

[0138] The results are given in Table 4. TABLE 4 Influence of thetemperature on polymerization in the presence of stable free nitroxylradical 1: 0.05 mol % based on vinyl chloride T Yield PD No. (° C.) (%)Mn Mw (Mw/Mn) control E 70 94 1.8 5.1 2.6 control F 80 93 1.0 2.6 2.5example 10 70 35 2.0 4.1 2.0 example 11 75 62 n.d. n.d. n.d. example 1280 56  1.25  2.86 2.3 example 13 85 43 n.d. n.d. n.d. example 14 90 431.6 3.5 2.2

EXPERIMENTAL DESCRIPTION OF THE REINITIATION EXAMPLES 15 THROUGH 22 ANDCONTROL EXPERIMENT G

[0139] Reinitiation experiments are carried out in a 100 mlSchlenck-tube. The solution which contains the respective PVC, a monomerand solvent (chlorobenzene) is degassed and heated for 15 h (Table 5) or21 h (Table 6) at the appropriate temperature indicated in table 5 and6, while stirring. After cooling in an ice bath, the polymer isprecipitated into 1500 ml methanol, filtered, washed with ethanol anddried under vacuum at 40° C. Molecular weights and polydispersity aredetermined by GPC (3 columns, PL Polymer Laboratories), calibrated withnarrow distributed polystyrene standards.

[0140] The following recipe is used:

[0141] 1.25 g PVC from example 7 and example 10

[0142] 20 ml chlorobenzene

[0143] 5 g comonomer as indicated in Tables 5 and 6, destabilized. TABLE5 Reinitiation and blockcopolymerization second T yield No. startingmaterial monomer (° C.) (%) Mn example 15 PVC from example 7 styrene 10030 53000 example 16 PVC from example 7 n-butyl- 130 25 28000 acrylate

[0144] TABLE 6 Reinitiation and block copolymerization Second monomer +Yield* Mn Mw No. optional additive T (° C.) (%) [× 10⁴] [× 10⁴] PDcontrol G PVC from example 10 130  91** 2.0 3.6 1.8 example 17 butylmethacrylate 130 41 2.4 6.0 2.5 example 18 styrene + acrylonitrile (1:3)110 15 2.4 7.2 3.0 example 19 styrene + MAA (1:1) + CSA 10 mg 130 100 Not determined example 20 styrene + MAI (1:1) + CSA 10 mg 130 68 3.0 7.92.7 example 21 methyl methacrylate + Stab. 10 mg 130 54 2.9 8.6 3.0example 22 butyl acrylate + Stab. 10 mg 120 22 1.9 3.9 2.0

[0145] Addition of CSA in the examples 19, 20 accelerates thepolymerization rate as known e.g. from U.S. Pat. No. 5,608,023.

[0146] Addition of stearyl-benzoyl-methane to the reaction solution inexample 21 and 22 results in reduced discoloration of the sampleaccording to improved thermal stability of the PVC polymer.

EXAMPLE 23 In-Situ Reinitiation with Butadiene

[0147] A suspension of 30 g vinyl chloride, 200 ml H₂O demin, 300 mgpoly vinyl alcohol (Mowiol 888) and 0.1 mol-% Initiator(1,1-dimethyl-2-ethylhexaneperoxoat) are stirred for 21 h reaction timeat 90° C. with 1000 rpm. The reactor is degassed by a nitrogen streamand vacuum and filled with 30 g butadiene. The reaction is stirred at90° C. for another 21 h. The product is isolated (7 g), purified andanalyzed as described above. Mn=19.000, Mw=39.000, PD=2.0.

1. A process for controlled free radical polymerization orcopolymerization of vinyl chloride at a temperature between 40° C. and95° C., at a pressure between 5 and 30 bar in the presence of a stablefree nitroxyl radical.
 2. A process according to claim 1, wherein thepolymerization or copolymerization is carried out in suspension.
 3. Aprocess according to claim 1, wherein the molar ratio of free radicalinitiator to stable free nitroxyl radical is from 100:1 to 1:10.
 4. Aprocess according to claim 1, wherein the stable free nitroxyl radicalis present from the beginning of the polymerization.
 5. A processaccording to claim 1, wherein the stable free nitroxyl radical is formedin situ during the polymerization reaction from the correspondingnitroxylether.
 6. A process according to claim 1, wherein the stablefree nitroxyl radical is a compound of formula A′, B′ or O′,

wherein m is 1, R is hydrogen, C₁-C₁₈alkyl which is uninterrupted orinterrupted by one or more oxygen atoms, cyanoethyl, benzoyl, glycidyl,a monovalent radical of an aliphatic carboxylic acid having 2 to 18carbon atoms, of a cycloaliphatic carboxylic acid having 7 to 15 carbonatoms, or an α,β-unsaturated carboxylic acid having 3 to 5 carbon atomsor of an aromatic carboxylic acid having 7 to 15 carbon atoms; p is 1;R₁₀₁ is C₁-C₁₂alkyl, C₅-C₇cycloalkyl, C₇-C₈aralkyl, C₂-C₁₈alkanoyl,C₃-C₅alkenoyl or benzoyl; R₁₀₂ is C₁-C₁₈alkyl, C₅-C₇cycloalkyl,C₂-C₈alkenyl unsubstituted or substituted by a cyano, carbonyl orcarbamide group, or is glycidyl, a group of the formula —CH₂CH(OH)-Z orof the formula —CO-Z or —CONH-Z wherein Z is hydrogen, methyl or phenyl;G₆ is hydrogen and G₅ is hydrogen or C₁-C₄alkyl, and G₁ and G₃ aremethyl and G₂ and G₄ are ethyl or propyl or G₁ and G₂ are methyl and G₃and G₄ are ethyl or propyl.
 7. A process according to claim 6, whereinin formula A′, B′ and O′ R is hydrogen, C₁-C₁₈alkyl, cyanoethyl,benzoyl, glycidyl, a monovalent radical of an aliphatic, carboxylicacid; R₁ is C₁-C₁₂alkyl, C₇-C₈aralkyl, C₂-C₁₈alkanoyl, C₃-C₅alkenoyl orbenzoyl; R₂ is C₁-C₁₈alkyl, glycidyl, a group of the formula—CH₂CH(OH)-Z or of the formula —CO-Z, wherein Z is hydrogen, methyl orphenyl.
 8. A process according to claim 1, wherein the stable freenitroxyl radical is of formula (Ic′), (Id′), (Ie′), (If′), (Ig′) or(Ih′)

wherein R₁, R₂, R₃ and R₄ independently of each other are C₁-C₁₈alkyl,C₃-C₁₈alkenyl, C₃-C₁₈alkinyl, C₁-C₁₈alkyl, C₃-C₁₈alkenyl, C₃-C₁₈alkinylwhich are substituted by OH, halogen or a group —O—C(O)—R₅, C₂-C₁₈alkylwhich is interrupted by at least one O atom and/or NR₅ group,C₃-C₁₂cycloalkyl or C₆-C₁₀aryl or R₁ and R₂ and/or R₃ and R₄ togetherwith the linking carbon atom form a C₃-C₁₂cycloalkyl radical; R₅, R₆ andR₇ independently are hydrogen, C₁-C₁₈alkyl or C₆-C₁₀aryl; R₈ ishydrogen, OH, C₁-C₁₈alkyl, C₃-C₁₈alkenyl, C₃-C₁₈alkinyl, C₁-C₁₈alkyl,C₃-C₁₈alkenyl, C₃-C₁₈alkinyl which are substituted by one or more OH,halogen or a group —O—C(O)—R₅, C₂-C₁₈alkyl which is interrupted by atleast one O atom and/or NR₅ group, C₃-C₁₂cycloalkyl or C₆-C₁₀aryl,C₇-C₉phenylalkyl, C₅-C₁₀heteroaryl, —C(O)-C₁-C₁₈alkyl, —O—C₁-C₁₈alkyl or—COOC₁—C₁₈alkyl; and R₉, R₁₀, R₁₁ and R₁₂ are independently hydrogen,phenyl or C₁-C₁₈alkyl.
 9. A process according to claim 8, wherein informula (Ic′), (Id′), (Ie′), (If′), (Ig′) and (Ih′) at least two of R₁,R₂, R₃ and R₄ are ethyl, propyl or butyl and the remaining are methyl;or R₁ and R₂ or R₃ and R₄ together with the linking carbon atom form aC₅-C₆cycloalkyl radical and one of the remaining substituents is ethyl,propyl or butyl.
 10. A process according to claim 1, wherein the stablefree nitroxyl radical has a hydrogen atom bound to the carbon atom inα-position to the nitrogen atom.
 11. A process according to claim 10,wherein the stable free nitrogen radical is a compound of formula


12. A process according to claim 5, wherein the nitroxylether from whichthe stable free nitroxyl radical is formed is of formula A, B or O,

wherein m is 1, R is hydrogen, C₁-C₁₈alkyl which is uninterrupted orinterrupted by one or more oxygen atoms, cyanoethyl, benzoyl, glycidyl,a monovalent radical of an aliphatic carboxylic acid having 2 to 18carbon atoms, of a cycloaliphatic carboxylic acid having 7 to 15 carbonatoms, or an α,β-unsaturated carboxylic acid having 3 to 5 carbon atomsor of an aromatic carboxylic acid having 7 to 15 carbon atoms; p is 1;R₁₀₁ is C₁-C₁₂alkyl, C₅-C₇cycloalkyl, C₇-C₈aralkyl, C₂-C₁₈alkanoyl,C₃-C₅alkenoyl or benzoyl; R₁₀₂ is C₁-C₁₈alkyl, C₅-C₇cycloalkyl,C₂-C₈alkenyl unsubstituted or substituted by a cyano, carbonyl orcarbamide group, or is glycidyl, a group of the formula —CH₂CH(OH)-Z orof the formula —CO-Z or —CONH-Z wherein Z is hydrogen, methyl or phenyl;G₆ is hydrogen and G₅ is hydrogen or C₁-C₄alkyl, G₁ and G₃ are methyland G₂ and G₄ are ethyl or propyl or G₁ and G₂ are methyl and G₃ and G₄are ethyl or propyl; and X is selected from the group consisting of—CH₂-phenyl, CH₃CH-phenyl, (CH₃)₂C-phenyl, (C₅-C₅cycloalkyl)₂CCN,(CH₃)₂CCN, CH₂CH═CH₂, CH₃CH—CH═CH₂ (C₁-C₄alkyl)CR₂₀—C(O)-phenyl,(C₁-C₄)alkyl-CR₂₀—C(O)—(C₁-C₄)alkoxy,(C₁-C₄)alkyl-CR₂₀—C(O)—(C₁-C₄)alkyl,(C₁-C₄)alkyl-CR₂₀—C(O)—N-di(C₁-C₄)alkyl,(C₁-C₄)alkyl-CR₂₀—C(O)—NH(C₁-C₄)alkyl, (C₁-C₄)alkyl-CR₂₀—C(O)—NH₂,wherein R₂₀ is hydrogen or (C₀-C₄)alkyl.
 13. A process according toclaim 12, wherein in formula A, B and O R is hydrogen, C₁-C₁₈alkyl,cyanoethyl, benzoyl, glycidyl, a monovalent radical of an aliphatic,carboxylic acid; R₁₀₁ is C₁-C₁₂alkyl, C₇-C₈aralkyl, C₂-C₁₈alkanoyl,C₃-C₅alkenoyl or benzoyl; R₁₀₂ is C₁-C₁₈alkyl, glycidyl, a group of theformula —CH₂CH(OH)-Z or of the formula —CO-Z, wherein Z is hydrogen,methyl or phenyl; and X is CH₃CH-phenyl.
 14. A process according toclaim 5, wherein the nitroxylether from which the stable free nitroxylradical is formed is of formula (Ic), (Id), (Ie), (If), (Ig) or (Ih)

wherein R₁, R₂, R₃ and R₄ independently of each other are C₁-C₁₈alkyl,C₃-C₁₈alkenyl, C₃-C₁₈alkinyl, C₁-C₁₈alkyl, C₃-C₁₈alkenyl, C₃-C₁₈alkinylwhich are substituted by OH, halogen or a group —O—C(O)—R₅, C₂-C₁₈alkylwhich is interrupted by at least one O atom and/or NR₅ group,C₃-C₁₂cycloalkyl or C₆-C₁₀aryl or R₁ and R₂ and/or R₃ and R₄ togetherwith the linking carbon atom form a C₃-C₁₂cycloalkyl radical; R₅, R₆ andR₇ independently are hydrogen, C₁-C₁₈alkyl or C₆-C₁₀aryl; R₈ ishydrogen, OH, C₁-C₁₈alkyl, C₃-C₁₈alkenyl, C₃-C₁₈alkinyl, C₁-C₁₈alkyl,C₃-C₁₈alkenyl, C₃-C₁₈alkinyl which are substituted by one or more OH,halogen or a group —O—C(O)—R₅, C₂-C₁₈alkyl which is interrupted by atleast one O atom and/or NR₅ group, C₃-C₁₂cycloalkyl or C₆-C₁₀aryl,C₇-C₉phenylalkyl, C₅-C₁₀heteroaryl, —C(O)—C₁-C₁₈alkyl, —O—C₁-C₁₈alkyl or—COOC₁-C₁₈alkyl; R₉, R₁₀, R₁₁, and R₁₂ are independently hydrogen,phenyl or C₁-C₁₈alkyl; and X is selected from the group consisting of—CH₂-phenyl, CH₃CH-phenyl, (CH₃)₂C-phenyl, (C₅C₆cycloalkyl)₂CCN,(CH₃)₂CCN, —CH₂CH═CH₂, CH₃CH—CH═CH₂ (C₁-C₄alkyl)CR₂₀—C(O)-phenyl,(C₁-C₄)alkyl-CR₂₀—C(O)—(C₁-C₄)alkoxy,(C₁-C₄)alkyl-CR₂₀—C(O)—(C₁-C₄)alkyl,(C₁-C₄)alkyl-CR₂₀—C(O)—(C₁-C₄)alkyl,(C₁-C₄)alkyl-CR₂₀—C(O)—N-di(C₁-C₄)alkyl,(C₁-C₄)alkyl—CR₂₀C(O)—NH(C₁-C₄)alkyl, (C₁-C₄)alkyl-CR₂₀—C(O)—NH₂,wherein R₂₀ is hydrogen or (C₁-C₄)alkyl.
 15. A process according toclaim 14, wherein in formula (Ic), (Id), (Ie), (f), (Ig) and (Ih) atleast two of R₁, R₂, R₃ and R₄ are ethyl, propyl or butyl and theremaining are methyl; or R₁ and R₂ or R₃ and R₄ together with thelinking carbon atom form a C₅-C₆cycloalkyl radical and one of theremaining substituents is ethyl, propyl or butyl.
 16. A processaccording to claim 1, wherein in a first step vinyl chloride ispolymerized and in a second step a different ethylenically unsaturatedmonomer is added to the polyvinyl chloride and block copolymerized toform an A-B block.
 17. A process according to claim 16, wherein thedifferent ethylenically unsaturated monomer is selected from the groupconsisting of of ethylene, propylene, n-butylene, i-butylene, styrene,substituted styrene, vinylpyridine, conjugated dienes, acrolein, vinylacetate, vinylpyrrolidone, vinylimidazole, maleic anhydride, maleinimidewhich may be unsubstituted at the nitrogen atom or substituted by alkylor aryl, (alkyl)acrylic acidanhydrides, (alkyl)acrylic acid salts,(alkyl)acrylicacid esters, (alkyl)acrylonitriles or (alkyl)acrylamides.18. A polyvinyl chloride macroinitiator having bound a thermally labilenitroxyl group via the oxygen atom, said macroinitiator being able tosplit into a polyvinyl chloride radical and a nitroxyl radical uponthermal treatment.
 19. A polyvinyl chloride block copolymer preparedaccording to claim
 16. 20. Use of a stable free nitroxyl radical forcontrolled free radical polymerization or copolymerization of vinylchloride at a temperature between 40° C. and 95° C., at a pressurebetween 5 and 30 bar.